Cocrystals of Barbituric Acid with Alkali Metal Halides

Barbituric acid BAH reacts with potassium, rubidium and caesium iodides in methanol, forming anhydrous BAH·MI. BAH·CsI has a different 8-fold coordination geometry from corresponding alkali metal bromides, intermediate between triangular dodecahedral and square antiprismatic. BAH·KI and BAH·RbI display features that are new for this family, with a high coordination number of 9, and with no involvement of iodide in either coordination or hydrogen bonding, its environment being six BAH molecules. BAH·NaCl·2H2O, prepared by successive treatment of BAH in water with sodium hydroxide and dilute hydrochloric acid, is isostructural with other chlorides and bromides, with 7-coordinate Na+ and a network of hydrogen bonding. Two BAH molecules are oxidatively coupled by aqueous potassium permanganate to generate 5-hydroxyhydurilic acid, isolated as a hydrated potassium salt with K+ in an unusually low 5-coordination. The folding of the BAH molecule in its full range of known crystal structures is analysed; the dihedral folding angle ranges from 0 to approximately 20 °, uncorrelated with any other particular features of the structures. This work is licensed under a Creative Commons Attribution 4.0 International License

N,N′-Bis(5-bromo­pyridin-2-yl)methane­diamine

The V-shaped title compound, C11H10Br2N4, lies on a crystallographic twofold rotation axis which passes through the central C atom. In the crystal, an infinite tape motif, which propagates in the a-axis direction, is formed by inversion-related N—H⋯N hydrogen-bonding inter­actions. The structure confirmed the identity of the compound as a reaction side product

3-(2,6-Dimethyl­anilino)imidazo[1,2-a]pyridin-1-ium perchlorate

The structure of the organic cation in the title compound, C15H16N3 +·ClO4 −, contains two essentially planar rings. Mean planes fitted through all non-H atoms of each ring system have an r.m.s. deviation of 0.019 Å for the imidazole-based ring and 0.016 Å for the 2,6-dimethyl­phenyl ring. The angle between the two planes is 86.76 (2)°. In the crystal structure, N—H⋯O inter­actions form a one-dimensional chain, which propagates in the b-axis direction. C—H⋯O inter­actions are also found in the crystal packing

Bis(tetraphenylphosphonium) di-μ-iodido-bis[diiodidopalladate(II)].

The title compound, (PPh4)2[Pd2I6], was obtained unintentionally as the product of an attempted synthesis of a tripalladium sandwich complex. The molecular dimensions are unexceptional and the Pd---Pd distance, at 3.8183 (12) A,is much too long for any Pd—Pd interaction. Pd has a typical square-planar coordination geometry and the centrosymmetric anion is essentially planar

Orthogonal Selection and Fixing of Coordination Self-Assembly Pathways for Robust Metallo-organic Ensemble Construction

Supramolecular construction strategies have overwhelmingly relied on the principles of thermodynamic control. While this approach has yielded an incredibly diverse and striking collection of ensembles, there are downsides, most obviously the necessity to trade-off reversibility against structural integrity. Herein we describe an alternative “assembly-followed-by-fixing” approach that possesses the high-yielding, atom-efficient advantages of reversible self-assembly reactions, yet gives structures that possess a covalent-like level of kinetic robustness. We have chosen to exemplify these principles in the preparation of a series of M₂L₃ helicates and M₄L₆ tetrahedra. While the rigidity of various bis­(bidentate) ligands causes the larger species to be energetically preferred, we are able to freeze the self-assembly process under “non-ambient” conditions, to selectivity give the disfavored M₂L₃ helicates. We also demonstrate “kinetic-stimuli” (redox and light)-induced switching between architectures, notably reconstituting the lower energy tetrahedra into highly distorted helicates